System and method for communicating over a wireless time-division duplex channel

ABSTRACT

According to the present invention, the bandwidth of a TDD channel is increased where multiple slave devices communicate with a master device over the channel. According to an aspect of the present invention, the master device can increase channel bandwidth by utilizing available transmit slots that occur during receipt of a multi-slot packet from a slave device. For example, the master device receives a first packet at a first frequency from a first slave via the channel. The master determines whether the first packet is a multi-slot packet, and if so, transmits a second packet to a second slave via the channel at a second frequency different from the first frequency. The second packet is transmitted after receipt of the first packet, but prior to the end of the first packet.

BACKGROUND

1. Field of the Invention

The present invention relates generally to wireless communications, andmore particularly to a system and method for communicating over atime-division duplex (TDD) channel.

2. Discussion of the Related Art

In today's electronically interconnected world, the normal complement ofelectronic equipment in the home or business includes devices that areconnected to one another in different ways. For example, many desktopcomputer systems have a central processing unit (CPU) connected to amouse, a keyboard, a printer and so on. A personal digital assistant(PDA) will normally connect to the computer with a cable and a dockingcradle. A television may be connected to a VCR and a cable box, with aremote control for all three components. A cordless phone connects toits base unit with radio waves, and it may have a headset that connectsto the phone with a wire. In a stereo system, a CD player, tape playerand record player connect to a receiver, which connects to speakers.These connections can be difficult to install and maintain, particularlyfor the lay user.

Alternatives to these conventional approaches to connectivity have beenproposed. Bluetooth™ (BT) is a computing and telecommunications industryspecification for connectivity that is both wireless and automatic, asdescribed in The Specification of the Bluetooth System, Version 1.1,Feb. 22, 2001, (“the BT specification”), which is incorporated herein byreference. BT allows any sort of electronic equipment—from computers andcell phones to keyboards and headphones—to make its own connections,without wires, cables or any direct action from a user. Because BTconnections are wireless, offices can be designed without regard tocable placement and users can travel with portable devices withouthaving to worry about carrying a multitude of cables. These connectionscan be established automatically, where BT devices find one another andform a connection without any user input at all.

BT requires that a low-cost microchip transceiver be included in eachdevice. The BT microchip transceiver communicates on a frequency of 2.45GHz, which has been set aside by international agreement for the use ofindustrial, scientific and medical devices (ISM). In addition to data,up to three voice channels are available. Each BT device has a unique48-bit device address from the Institute of Electrical and ElectronicsEngineers 802 standard. Connections can be point-to-point ormulti-point. Data can be exchanged at a rate of 1 megabit per second (upto 2 Mbps in the second generation of the technology).

A number of common consumer devices also take advantage of the same RFband. Baby monitors, garage-door openers and some cordless phones allmake use of frequencies in the ISM band. The BT design employs varioustechniques to reduce interference between these devices and BTtransmissions. For example, BT avoids interfering with other systems bysending out relatively weak signals of 1 milliwatt. By comparison, somecell phones can transmit a signal of 3 watts. The low power limits therange of a BT device to about 10 meters, thereby reducing theprobability of interference with other devices.

BT also employs a spread-spectrum frequency hopping scheme to furtherreduce interference and increase capacity. BT devices use 79 randomlychosen frequencies within a designated range, changing from one toanother on a regular basis 1,600 times every second. The randomfrequency hopping pattern makes it unlikely that two BT transmitterswill be on the same frequency at the same time, thus reducing theprobably of BT devices interfering with one another. This technique alsominimizes the risk that other non-BT devices such as portable phones orbaby monitors will disrupt BT devices since any interference on aparticular frequency will last only a fraction of a second.

When BT devices come within range of one another, an electronicconversation takes place to determine whether they have data to share orwhether one needs to control the other. Once the conversation hasoccurred, the devices form a “piconet”. A piconet may link deviceslocated throughout a room, such as a home entertainment system, ordevices much closer together such as a mobile phone on a belt-clip and aheadset, or a computer, mouse, and printer. Once a piconet isestablished, the connected devices randomly hop frequencies in unison tocommunicate with one another and avoid other piconets that may beoperating nearby.

One device acts as the master of the piconet, whereas the other unit(s)acts as slave(s). Up to seven slaves can be active in a single piconet.The slaves synchronize to the master's timing, and access to the channelis controlled by the master. The channel is represented by apseudo-random hopping sequence hopping through the 79 RF channels. Thehopping sequence is unique for each piconet and is determined by the BTdevice address of the master; the phase in the hopping sequence isdetermined by the BT clock of the master. The channel is divided intotime slots where each slot corresponds to an RF hop frequency.Consecutive hops correspond to different RF hop frequencies. The nominalhop rate is 1,600 hops/second. All BT devices participating in thepiconet are time- and hop-synchronized to the channel.

The channel is divided into time slots, each 625 μs in length. The timeslots are numbered according to the BT clock of the piconet master. Theslot numbering ranges from 0 to 27²−1 and is cyclic with a cycle lengthof 2²⁷. In the time slots, master and slave can transmit packets.According to the BT specifications, a TDD scheme is used where masterand slave alternatively transmit. The master starts its transmission ineven-numbered time slots only, and the slaves starts their transmissionsin odd-numbered time slots only. The packet start is aligned with theslot start. Packets transmitted by the master or the slaves may extendover up to five time slots.

The RF hop frequency shall remain fixed for the duration of the packet.For a single packet, the RF hop frequency to be used is derived from thecurrent BT clock value. For a multi-slot packet, the RF hop frequency tobe used for the entire packet is derived from the BT clock value in thefirst slot of the packet. The RF hop frequency in the first slot after amulti-slot packet uses the frequency as determined by the current BTclock value. If a packet occupies more than one time slot, the hopfrequency applied is the hop frequency as applied in the time slot wherethe packet transmission was started.

Between master and slave(s), different types of links can beestablished. Two link types have been defined in the BT specifications:Synchronous Connection-Oriented (SCO) links, and AsynchronousConnection-Less (ACL) links. The SCO link is a point-to-point linkbetween a master and a single slave in the piconet. The master maintainsthe SCO link by using reserved slots at regular intervals. The ACL link,by comparison, is a point-to-multipoint link between the master and allthe slaves participating on the piconet. In the slots not reserved forSCO links, the master can exchange packets with any slave on a per-slotbasis. The ACL link provides a packet-switched connection between themaster and all active slaves participating in the piconet.

Data on the piconet channel is conveyed in packets. Each packet consistsof three entities: the access code, the header, and the payload. Theaccess code and header are of fixed size: 72 bits and 54 bitsrespectively. The payload can range from zero to a maximum of 2745 bits.Packets may include the access code only, the access code header, or theaccess code header payload. Sixteen different types of packets can bedistinguished, four of which are pre-defined control types that arecommon to both link types. A 4-bit TYPE code, included in the header,specifies which packet type is used. The interpretation of the TYPE codedepends on the physical link type associated with the packet. The devicefirst determines whether the packet is sent on an SCO link or an ACLlink, and then determines which type of SCO packet or ACL packet hasbeen received. The TYPE code also indicates how many slots the currentpacket will occupy.

In an ACL link, the master can either broadcast packets to every slavein the piconet, or send packets to a particular slave. ACL packets notaddressed to a specific slave are considered as broadcast packets andare read by all the slaves. In the reverse direction, the mastercontrols slave access to the channel. According to the BT specification,under normal operating conditions only one slave transmits over thepiconet channel during any particular time slot. The slaves thereforeshare the available bandwidth in the slave-to-master direction of theTDD channel.

In many applications, piconets are formed that include a relatively fewnumber of slaves. For example, a computer can act as a master in apiconet with a slave printer or mouse. Here, the sharing of bandwidthamongst the slaves may not result in any significant degradation ofperformance. However, other scenarios may require that a master supporta piconet having a greater number of slaves. For example, a networkaccess point (NAP) provides wireless access to a network, such as theInternet or a local area network (LAN), to those BT devices within rangeof the NAP. NAPs can be used to provide convenient wireless access tothe Internet, email, and other LAN resources. In typical businessenvironments, and even some home environments, the NAP can often beexpected to support up to the maximum 7 slaves. Performance inenvironments such as this can suffer where a relatively large number ofslaves are sharing the available channel bandwidth.

What is needed therefore is an improved system and method wherebychannel bandwidth is increased for those piconets having multipleslaves.

SUMMARY OF THE INVENTION

The present invention satisfies this need by providing a system andmethod for increasing the bandwidth of a TDD channel where multipleslave devices communicate with a master device over the channel. Amaster device can increase channel bandwidth by utilizing availabletransmit slots that occur during receipt of a multi-slot packet from aslave device. For example, the master device receives a first packet ata first frequency from a first slave via the channel. The masterdetermines whether the first packet is a multi-slot packet, and if so,transmits a second packet to a second slave via the channel at a secondfrequency different from the first frequency. The second packet istransmitted after receipt of the first packet, but prior to the end ofthe first packet.

These and other aspects of the present invention will become apparentfrom the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1 depicts an example wireless communications environment withinwhich various example embodiments of the present invention operate.

FIG. 2 depicts an example slave device in greater detail.

FIG. 3 depicts a master device in greater detail according to an exampleembodiment of the present invention.

FIG. 4 depicts a flowchart that describes the operation of a masterdevice according to an example embodiment of the present invention.

FIG. 5 depicts a timing diagram that illustrates example operationsaccording to the present invention using a master device having tworadios.

FIG. 6 depicts a timing diagram that illustrates example operationsaccording to the present invention using a master device having threeradios.

FIG. 7 depicts a timing diagram that illustrates a master devicetransmitting a new packet after completing a previous multi-slottransmission.

FIG. 8 depicts an example wireless environment wherein multiple slavedevices communicate with a NAP to gain access to network resources.

FIG. 9 depicts a NAP in greater detail according to an exampleembodiment of the present invention.

DETAILED DESCRIPTION

The present invention provides a system and method for increasing thebandwidth of a TDD channel where multiple slaves communicate with amaster over the channel. Generally speaking, according to the presentinvention wireless devices acting in the role of master utilize transmitopportunities that occur during reception of a multi-slot packet.Additional radios can be added to the master device to transmit theadditional packets. Utilizing techniques according to the presentinvention, the master transmits over the channel while at the same timereceiving a multi-slot packet with no interference between thetransmissions. According to the BT specification, by comparison, onlyone device within a particular piconet transmits over the channel at anygiven time. Techniques according to the present invention effectivelyincrease channel bandwidth relative to standard BT operation withoutviolating the BT specification.

Example embodiments of the present invention in many instances aredescribed herein in the context of an example BT communicationsenvironment. These techniques are applied to the BT environment forillustrative purposes only, and should not be construed as limited tothis environment. Rather, it will be apparent to those of skill in therelevant art that the principles described herein can also be applied toother similar wireless communications environments wherein master andslave devices communicate over a TDD channel.

FIG. 1 depicts an example wireless communications environment 100 withinwhich various example embodiments of the present invention operate. Amaster device 102 communicates with two or more slave devices 104 (shownas 104A and 104B). Wireless links 110 (shown as 110A and 110B) areestablished between master device 102 and each of the slave devices 104.The wireless links 110 together form a channel 120, and the masterdevice 102 and slave devices 104 together form a wireless network 130.In the example BT environment, wireless links 110 represent short-rangeRF links wherein master and slave devices communicate according to theprotocols described in the BT specification. Further, wireless network130 represents a piconet, and channel 120 represents the TDD channeldescribed in the BT specification. Various techniques according to thepresent invention are described herein for increasing the bandwidth ofchannel 120.

Master device 102 and slave devices 104 represent electronic devicesthat are each equipped with at least one wireless radio capable ofestablishing and exchanging information over wireless link 110. Thesedevices can, for example, represent a wide range of consumer electronicdevices such as a laptop computer, PDA, cordless telephone, stereoequipment, television or VCR. As will be apparent, these devices canrepresent both portable and non-portable devices. Master device 102 andslave devices 104 can represent identically or similarly configureddevices that have been equipped according to the present invention. Forexample, master device 102 and slave devices 104A and 104B can representthree laptop computers in communication with one another, where one ofthe laptops is configured as master device 102 and the others as slavedevices 104. Alternatively, master device 102 and slave devices 104 canrepresent dissimilar devices. For example, master device 102 mightrepresent a laptop computer, slave device 104A a printer, and slavedevice 104B a PDA.

Though slave devices 104 are in some way subservient to master device102, the precise roles of master and slave devices can vary according tothe communication protocols followed within wireless network 130. In theexample BT environment, slave devices 104 within a piconet synchronizeto the timing of master device 102. Furthermore, access to channel 120is controlled by master device 102. As will be apparent, many of thedetails concerning the master and slave roles are not pertinent to theoperation of the various example embodiments of the present inventiondescribed herein. The master and slave roles are therefore described tothe extent that they are pertinent. Techniques according to the presentinvention can be applied to other environments wherein the roles ofmaster and slave are similarly defined.

The designation of one wireless device as master and the others asslaves can depend, at least in part, on the communication protocol(s)followed within wireless network 130. For example, according to the BTspecification the wireless device that performs the paging procedure isinitially designated as the master device, and the device that is pagedis designated the slave device. However, various procedures are alsodefined for swapping master and slave roles. Furthermore, a wirelessdevices that acts as a master in one piconet can simultaneously act as aslave in another piconet. The techniques described herein according tothe present invention can therefore be applied to whichever devicehappens to be acting in the role of master at any given time.

These techniques can be applied within many different specificconfigurations of wireless communications environment 100 to increasethe bandwidth of channel 120. These techniques are particularlyapplicable to those environments where master devices 102 commonlycommunicate with a relatively large number of slave devices 104 within awireless network. In the example BT environment, a piconet master cansupport up to seven active slave devices. The techniques describedherein potentially provide increasingly greater bandwidth improvements(relative to the performance achieved through normal operation accordingto the BT specification) as the number of slaves in a piconet approachesthe maximum of seven.

FIG. 2 depicts an example slave device 104 in greater detail. Slavedevice 104 includes a wireless transceiver 202 that provides wirelesscommunication capability to a host system 204. Host system 204represents the device that employs wireless transceiver 202 tocommunicate data via wireless link 110. Example host systems 202 caninclude both sophisticated computing devices such as a personal computeror PDA running a wide variety of software, as well as less sophisticateddevices such as a VCR or audio speaker. Equipped with wirelesstransceiver 202, these host systems are able to communicate wirelesslywith other similarly equipped devices.

Wireless transceiver 202 establishes and communicates information (e.g.,data, voice) via wireless link 110. In the example BT environment,wireless transceiver 202 can represent a BT microchip transceiver, suchas the Bluetooth™ Module (part number ROK 101 007) produced by Ericsson.According to the BT specification, wireless transceiver 202 includes a2.4 GHz radio 210, a link control 212, and a link manager 214. Linkcontrol 212 represents the software that carries out the basebandprotocols and other low-level link routines. Link manager 214 representsa support unit for link management and host terminal interfacefunctions. Link manager 214 implements the link manager protocol,including link layer messages for link set-up and control. Radio 210provides the RF interface between host system 204 and wireless link 110.

FIG. 3 depicts master device 102 in greater detail according to anexample embodiment of the present invention. As with slave device 104,master device 102 includes a wireless transceiver 302 that provideswireless communication capability to a host system 304. Host system 304includes an application 310 representing the software that directs theoperation of wireless transceiver 304. Application 310 can include, forexample, program code for directing master device 102 to perform thetechniques described herein. Host system 304 communicates with wirelesstransceiver 302 via a link 320 according to a pre-defined protocol. Inthe example BT environment, link 320 represents a universal asynchronousreceiver transmitter (UART) serial link, where host system 304 andwireless transceiver 302 communicate using the host controller interface(HCI) protocol defined in the BT specification.

The present invention can include one or more computer programs whichcause wireless devices to perform the functions described herein andillustrated in the appended flowcharts. However, it should be apparentthat there could be many different ways of implementing the invention incomputer programming, or a combination of hardware and software, and theinvention should not be construed as limited to any one set of computerprogram instructions. Further, a skilled programmer would be able towrite such a computer program to implement the disclosed inventionwithout difficulty based on the flowcharts and associated writtendescription included herein. Therefore, disclosure of a particular setof program code instructions is not considered necessary for an adequateunderstanding of how to make and use the invention.

Wireless transceiver 302 includes two or more radios 210 (shown as 210Aand 210B) in addition to link manager 214 and link control 212. As willnow be described in greater detail, having additional radios 210 allowsmaster device 102 to utilize transmit slots during a multi-slot packetsend by a slave device.

FIG. 4 depicts a flowchart 400 that describes the operation of masterdevice 102 according to an example embodiment of the present invention.These operations will be described in the context of the example BTenvironment, and in conjunction with FIGS. 5, 6, and 7 which depictexample timing diagrams. Timing diagram 500 depicted in FIG. 5 isdivided into ten time slots, labeled T1 through T10, that representexample time slots from channel 120 that could occur anywhere within thehop code. Channel 120 is divided into time slots where each slotcorresponds to an RF hop frequency. Consecutive hops correspond todifferent RF hop frequencies. According to the TDD scheme described inthe BT specification, master device 102 and slave devices 104 transmitin alternating time slots over channel 120. Master device 102 can startits transmissions in even-numbered time slots only, whereas slavedevices 104 can start their transmissions in odd-numbered time slotsonly. Packets transmitted by master device 102 or slave devices 104 mayextend over up to five time slots. The RF hop frequency remains fixedfor the duration of the packet. Single-slot packets use the RF hopfrequency associated with the slot during which the packet istransmitted. For a multi-slot packet, the entire packet is transmittedat the RF frequency associated with the first slot of the packet.

Consider example wireless environment 100, wherein master device 102 isin communication with slave devices 104A and 104B. Master device 102 hasestablished wireless links 110A and 110B according to the proceduresdescribed in the BT specification. Slave devices 104A and 104B are alsooperating in accordance with the BT specification, and are thereforesharing the bandwidth of the TDD channel 120 with master device 102.

In operation 402, master device 102 receives a first packet from a firstslave device 104. This first packet is transmitted at the RF hopfrequency corresponding to the first time slot that the packet occupies.For example, assume that master device 102 receives a packet from slavedevice 104A via wireless link 110A. This packet is shown as packet A inFIG. 5. Packet A is sent by slave device 104A and received by masterdevice 102 during time slot T1. Packet A is transmitted at a frequencyf1 corresponding to time slot T1. The propagation delay is negligible,given that wireless link 110A represents a short-range wirelessconnection.

In operation 404, master device 102 determines whether the first packetis a multi-slot packet. As will be apparent, this determination can bemade in a number of different ways, depending upon the particularcommunication protocols employed within channel 120. For example,according to the BT specifications, master device 102 can determinewhether a packet is a multi-slot packet by examining the packet header.The BT specification provides for twelve different packet types that canbe defined for each of the SCO and ACL link types. A 4-bit TYPE code isincluded in the packet header to indicate the different packets on alink. Packets occupying one, three, and five time slots have beendefined in the BT specifications. Master device 102 can infer theslot-length of a packet received from a slave device by decoding thepacket header and examining the TYPE code. Packets occupying three orfive time slots are determined to be multi-slot packets.

In example timing diagram 500, master device 102 decodes the header ofpacket A, and examines the packet type code which indicates that packetA has a length of five slots. Master device 102 therefore determinesthat packet A is a multi-slot packet.

In operation 406, master device 102 transmits a second packet to asecond slave device prior to the end of the first packet. The secondpacket can be of any allowable length. Under normal BT operatingconditions, master device 102 waits until the first slave devicefinishes transmitting the first packet before beginning to transmit thenext packet. As applied to example timing diagram 500, master device 102would wait until time slot T6 before transmitting packet B. Furthermore,master devices 102 having a single radio 210 would be unable to transmita second packet while simultaneously receiving the first packet.

However, according to the present invention, master device 102 beginstransmitting a second packet to a second slave device (any slave in thepiconet other than the first slave), and if this second transmissionoccurs prior to the end of the first packet, then channel bandwidth isincreased. According to the BT specification, even though the firstslave is transmitting a multi-slot packet, all the other slaves in thepiconet will be listening during even-numbered time slots at thecorresponding frequencies for transmissions from the master. As aresult, master device 102 can begin transmitting a second packet duringany even numbered time slot and the slave device to which the packet isdirected will be listening at the correct frequency. If master device102 begins transmission of the second packet prior to the end of thefirst packet, the effective bandwidth of channel 120 is increased. Thissecond packet can be sent to any slave in the piconet other than thefirst slave that is already engaged in transmitting the first packet.Moreover, the transmission of the second packet will not interfere withthe first packet because they are being transmitted at differentfrequencies. Therefore, according to the present invention, masterdevice 102 utilizes available transmit slots during a multi-slot packetsend by a slave to send packets to another slave, resulting in increasedchannel bandwidth.

For example, referring to timing diagram 500, master device 102 beginstransmitting packet B to slave 104B in time slot T2 at a frequency f2.The transmission of packet B does not interfere with packet A, becausefrequency f2 is different than frequency f1. Master device 102 couldalternatively begin transmitting packet B to slave 104B in time slot T4at a frequency f4. In either event, the bandwidth of channel 120 isincreased, though there is a potential for additional increases inbandwidth if the earlier time slot is used.

According to an example embodiment of the present invention, masterdevice 102 is equipped with at least one additional radio 210 in orderto transmit the second packet prior to the end of the first multi-slotpacket. Referring back to example master device 102 depicted in FIG. 3,radio 210A can be used, for example, to receive packet A during timeslots T1 through T5, while radio 210B is used to transmit packet Bbeginning at time slot T2 or T4.

Operations 402 through 406 can be repeated for each packet that isreceived by master device 102, so long as master device 102 has anavailable radio 210 that is not currently in use either transmitting orreceiving a packet. For example, as shown in timing diagram 500, masterdevice 102 receives packet C from slave 104B during time slot T3. Masterdevice 102 employs radio 210B to receive packet C. In operation 404,master device 102 determines that packet C is a multi-slot packet. Ifmaster device 102 is only equipped with two radios 210, master device102 must wait until one of the radios is available before transmittingthe next packet. This scenario is depicted in timing diagram 500. Attime slot T3, radio 210A is still busy receiving packet A and radio 210Bis busy receiving packet C. Radio 210A becomes available in time slot T6upon finishing receipt of packet A in time slot T5 As shown, masterdevice 102 therefore employs radio 210A in time slot T6 to transmitpacket D to slave device 104A.

However, if master device 102 is equipped with a third radio 210C (notshown), then master device 102 may begin transmitting the next packetwithout waiting for either radio 210A or 210B to become available. FIG.6 depicts an example timing diagram 600 that illustrates this scenario.As shown in FIG. 6, master device 102 employs radio 210C to begintransmitting packet D during time slot T4 to a third slave device 104C(not shown) in piconet 130. Therefore, at time slot T4 radio 210A isreceiving packet A from slave 104A, radio 210B is receiving packet Cfrom slave 104B, and radio 210C is transmitting packet D to slave 104C.Radio 210C then begins receiving a three-slot packet (packet E) fromslave 104C during time slot T5 In operation 404, master 102 determinesthat packet E is a multi-slot packet, and that radio 210A will beavailable in time slot T6 for additional transmissions. In this manner,operations 402 through 406 are repeated to employ radios 210 as theybecome available.

According to the BT specification, slave devices 104 do not listen fortransmissions from the master upon determining that the master istransmitting a multi-slot packet. As a result, in the example BTenvironment, master device 102 should not begin to transmit a new packetonce the master is in the midst of a multi-slot transmission, even if aradio is available. This is because slave devices 104, operatingaccording to the BT specification, won't be listening during this time.FIG. 7 depicts a timing diagram 700 that illustrates this scenario. Inthis example, packet D is a three-slot packet. Master device 102 beginstransmitting packet D to slave 104C at time slot T4 At time slot T6,radio 210A is available after finishing the transmission of packet A intime slot T5. Master 102 could therefore employ radio 210A to begintransmitting a new packet at time slot T6. However, the slaves allreceived packet D, determined that master device 102 was transmitting amulti-slot packet, and therefore sleep for the remainder of the packet Dtransmission. The slave devices 102 only begin to listen again fortransmissions from the master in the next available master transmit slotafter awakening, i.e., time slot T8 So, according to an exampleembodiment of the present invention, master device 102 waits until itfinishes transmitting the multi-slot packet D before transmitting newpacket F in time slot T8 As shown in FIG. 7, master device 102 beginsreceiving packet E from slave C in time slot T7.

When determining the number of radios 210 to include within masterdevice 102, there is a tradeoff between expense (e.g., in terms of cost,complexity, chip real estate) and capabilities. Adding additional radios210 may result in increased channel bandwidth, but will increaseexpenses associated with master device 102. In the example BTenvironment, master devices 102 having two radios 210 represents a goodcompromise between these cost/benefit tradeoffs. In any event, giventhat the maximum length of packets defined by the BT specification isfive time slots and that masters are only allowed to begin transmittingevery other slot, no additional benefits are gained by having more thanthree radios 210 in any single master device 102.

According to another example embodiment of the present invention, thetechniques described herein can be at least partially implemented byadding a receive-only radio (not shown) to master device 102. Referringback to example timing diagram 500 in FIG. 5, master device 102 couldemploy the receive-only radio to receive packet A at time slot T1.Master device 102 could then employ radio 210 to transmit packet Bduring time slot T2, and then to receive packet C at time slot T3.However, once the receive-only radio has completed reception of packet Aat time slot T5, master device 102 will not be able to transmit anotherpacket in the next available master transmit slot, T6. This is becausethe receive-only radio is not capable of transmitting, and the otherradio 210 is still busy receiving packet C. Master device 102 couldtherefore transmit the next packet at time slot T8, once packet C hasbeen completely received at time slot T7.

The techniques according to the present invention for increasing channelbandwidth are particularly applicable in situations where a particularwireless device is known to operate as a master in piconets havingmultiple slaves. FIG. 8 depicts just such an environment, wherein slavedevices 104 communicate with a NAP 802 to gain access to a network 810.NAP 802 can be used, for example, within a home or business to providewireless access to network resources. Network 810 can represent, forexample, the Internet, a LAN, or any other communications network overwhich data may be exchanged. NAPs 802 will commonly be expected tosimultaneously support connections to multiple devices. According to theBT specification, any wireless device that supports simultaneousconnections must be the piconet master. NAPs 202 must therefore act as amaster device 102, and those devices attempting to gain network accessact as slave devices 104.

FIG. 9 depicts NAP 802 in greater detail according to an exampleembodiment of the present invention. As shown in FIG. 9, NAP 802includes link manager 214, link control 212, and two or more radios 210.NAP 802 further includes a network interface 902 for communicating withnetwork 810. Here, network interface 902 is analogous to the host systemdescribed above with respect to FIG. 3.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. While the invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention.

1. A method for communicating over a time-division duplex channel,comprising: (a) receiving a first packet at a first frequency from afirst slave device via the channel, wherein said first packet isreceived beginning at a first slot; and (b) determining whether saidfirst packet is a multi-slot packet, and if so, transmitting a secondpacket to a second slave device via the channel at a second frequencydifferent from said first frequency, wherein said second packet istransmitted after said first slot and prior to the end of said firstpacket.
 2. The method of claim 1, wherein said first packet comprises aheader having a packet type code indicative of the slot length of saidfirst packet, and said determining comprises inferring whether saidfirst packet is a multi-slot packet based on said packet type code. 3.The method of claim 1, wherein said second packet is transmitted duringa first available transmit slot.
 4. A computer readable media embodyinga method for communicating over a time-division duplex channel, themethod comprising: (a) receiving a first packet at a first frequencyfrom a first slave device via the channel, wherein said first packet isreceived beginning at a first slot; and (b) determining whether saidfirst packet is a multi-slot packet, and if so, transmitting a secondpacket to a second slave device via the channel at a second frequencydifferent from said first frequency, wherein said second packet istransmitted after said first slot and prior to the end of said firstpacket.
 5. The computer readable media of claim 4, wherein said firstpacket comprises a header having a packet type code indicative of theslot length of said first packet, and said determining comprisesinferring whether said first packet is a multi-slot packet based on saidpacket type code.
 6. The computer readable media of claim 4, whereinsaid second packet is transmitted during the first available transmitslot.
 7. A wireless device for communicating over a time-division duplexchannel, said wireless device comprising: (a) a first radio configuredto receive a multi-slot packet at a first frequency from a first slavevia the channel, wherein said multi-slot packet is received during afirst slot; (b) means for determining whether said first packet is amulti-slot packet; and (c) a second radio configured to transmit asecond packet to a second slave responsive to said means making apositive determination, wherein said second packet is transmitted viathe channel at a second frequency different from said first frequencyafter said first slot and prior to the end of said first packet.
 8. Thewireless device of claim 7, wherein said wireless device acts as amaster to said first slave and said second slave.
 9. The wireless deviceof claim 7, wherein said wireless device comprises a network accesspoint coupled to a network.
 10. The wireless device of claim 7, whereinsaid first radio comprises a receive-only radio.
 11. The wireless deviceof claim 7, wherein said first and second radios comprise 2.4 GHzBluetooth radios.
 12. The wireless device of claim 7, wherein said firstpacket comprises a header having a packet type code indicative of theslot length of said first packet, and said means for determiningcomprises means for inferring whether said first packet is a multi-slotpacket based on said packet type code.
 13. The wireless device of claim7, wherein said second packet is transmitted during the first availabletransmit slot.
 14. A system comprising: (a) a time-division duplexchannel; (b) a first slave device configured to transmit a first packetover said time-division duplex channel at a first frequency during afirst time slot; (c) a master device, configured to receive said firstpacket, to determine whether said first packet is a multi-slot packet,and if so, to transmit a second packet over said time-division duplexchannel at a second frequency different from said first frequency,wherein said second packet is transmitted after said first slot andprior to the end of said first packet; and (d) a second slave deviceconfigured to receive said second packet.
 15. The system of claim 14,wherein said master device is master of a piconet that includes saidfirst slave and said second slave.
 16. The system of claim 14, whereinsaid master device comprises a network access point coupled to anetwork.
 17. The system of claim 14, wherein said first packet comprisesa header having a packet type code indicative of the slot length of saidfirst packet, and wherein said master device is configured to inferwhether said first packet is a multi-slot packet based on said packettype code.
 18. The system of claim 14, wherein said second packet istransmitted during the first available transmit slot.